Biology Reference
In-Depth Information
Figure 6.1 Spinozonocol-
pites prominatus (Nypa)
from the Eocene Laredo
Formation (Claiborne
Group; Casa Blanca fl ora
and fauna), Webb County,
southeastern Texas. From
Westgate and Gee 1990.
Used with permission from
Elsevier Science Publishers,
Amsterdam.
nozonocolpites
) and a pollen type of unknown affi nities called
Brevitricolpites
variabilis
in northern South America are found in lignite sediments. But in
the middle to late Eocene, these species disappeared and
Rhizophora
became
the prominent member of mangrove vegetation. This transition converted
pre-middle Eocene brackish-water coastal communities to essentially mod-
ern counterparts of mangrove vegetation. Thus, the mangrove community
joins the coniferous forest of western montane northern North America as
another modern ecosystem appearing in the middle Eocene. Also present
was the lowland neotropical rain forest from Paleocene times, along with
communities of freshwater aquatic plants, present in the Cretaceous and
diverse, for example, in the middle Eocene Princeton chert (Cevallos-Ferriz
et al. 1991). There was a limited but expanding deciduous forest differenti-
ating from the old polar broad-leaved deciduous forest and coalescing with
elements elsewhere. Likely present in near-modern aspect was a freshwater
herbaceous bog/marsh/swamp and, diffi cult to detect because of poor ta-
phonomic (preservation) conditions, a beach/strand/dune plant formation.
Versions of the shrubland/chaparral-woodland-savanna were present in the
Green River fl ora, and briefl y in the southeastern United States as a dry
tropical forest during the middle Eocene. This makes eight of the twelve
New World ecosystems, or recognizable variations, present by the end of
the early Miocene, along with elements of four others (desert, grassland,
alpine tundra, and tundra). The latter two coalesced as conditions became
colder and drier later in the Tertiary.
